U.S. patent application number 12/087422 was filed with the patent office on 2009-02-19 for production process of 1,6-hexanediol.
Invention is credited to Hirofumi Ii, Tomoyuki Ito, Yoshiki Kawamura, Toshiyuki Matsushita.
Application Number | 20090048471 12/087422 |
Document ID | / |
Family ID | 38256352 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090048471 |
Kind Code |
A1 |
Ii; Hirofumi ; et
al. |
February 19, 2009 |
Production Process of 1,6-Hexanediol
Abstract
A method is provided for obtaining highly pure 1,6-hexanediol in
which the contents of impurities such as 1,4-cyclohexanediol,
1,5-hexanediol, 1,2-cyclohexanediol, 1,7-pentanediol,
1,5-pentanediol and high boiling point components are significantly
reduced. This process for producing 1,6-hexanediol from cyclohexane
comprises the steps of: (1) treating an aqueous extraction
concentrate of a reaction mixture obtained by oxidation of
cyclohexane with a lower alcohol to esterify monocarboxylic acids
and dicarboxylic acids contained in the extract, and simultaneously
remove and separate by distillation water, excess lower alcohols
and carboxylic acid esters; (2) converting oligomer esters
contained in the bottom liquid to carboxylic acid esters by
depolymerizing the oligomer esters at a high temperature and high
pressure in the presence of a lower alcohol and a catalyst; and (3)
hydrogenating the carboxylic acid esters distilled off in the step
(1) and the carboxylic acid esters obtained in the step (2) either
respectively or collectively to convert to 1,6-hexanediol.
Inventors: |
Ii; Hirofumi; (Yamaguchi,
JP) ; Ito; Tomoyuki; (Yamaguchi, JP) ;
Kawamura; Yoshiki; (Yamaguchi, JP) ; Matsushita;
Toshiyuki; (Yamaguchi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
38256352 |
Appl. No.: |
12/087422 |
Filed: |
January 12, 2007 |
PCT Filed: |
January 12, 2007 |
PCT NO: |
PCT/JP2007/050286 |
371 Date: |
July 3, 2008 |
Current U.S.
Class: |
568/884 |
Current CPC
Class: |
C07C 67/03 20130101;
C07C 67/08 20130101; C07C 67/03 20130101; C07C 67/08 20130101; C07C
67/08 20130101; C07C 29/149 20130101; C07C 29/80 20130101; C07C
29/80 20130101; C07C 29/149 20130101; C07C 69/675 20130101; C07C
31/20 20130101; C07C 31/20 20130101; C07C 67/03 20130101; C07C
69/44 20130101; C07C 69/44 20130101; C07C 69/675 20130101 |
Class at
Publication: |
568/884 |
International
Class: |
C07C 29/48 20060101
C07C029/48 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 13, 2006 |
JP |
2006-005802 |
Claims
1. A process for producing 1,6-hexanediol from cyclohexane,
comprising the steps of: (1) treating an aqueous extraction
concentrate of a reaction mixture obtained by oxidation of
cyclohexane with a lower alcohol to esterify monocarboxylic acids
and dicarboxylic acids contained in the extract, and simultaneously
remove and separate by distillation water, excess lower alcohols
and carboxylic acid esters; (2) converting oligomer esters
contained in the bottom liquid to carboxylic acid esters by
depolymerizing the oligomer esters at a high temperature and high
pressure in the presence of a lower alcohol and a catalyst; and,
(3) hydrogenating the carboxylic acid esters distilled off in the
step (1) and the carboxylic acid esters obtained in the step (2)
either respectively or collectively to convert to
1,6-hexanediol.
2. The process according to claim 1, wherein the esterification is
carried out in the form of a gas-liquid reaction in the step
(1).
3. The process according to claim 1, wherein the esterification is
carried out at 0 to 5 MPa in the step (1).
4. The process according to claim 1, wherein the depolymerization
of the oligomer esters of step (2) is carried out using oligomer
esters having an acid value of 30 mgKOH/g or less.
5. The process according to claim 1, wherein the depolymerization
in the step (2) is carried out at a pressure higher than the vapor
pressure curve of the oligomer esters.
6. The process according to claim 1, wherein the depolymerization
in the step (2) is carried out in the liquid phase under conditions
of 250 to 280.degree. C. and 9 to 15 MPa.
7. The process according to claim 1, wherein the carboxylic acid
esters obtained in the steps (1) and (2) are further supplied to
distillation either separately or collectively.
8. The process according to claim 7, wherein the bottom liquid
obtained following the distillation of the carboxylic acid esters
is further depolymerized to convert to carboxylic acid esters
followed by supplying to hydrogenation.
Description
TECHNICAL FIELD
[0001] The present invention relates to a production process of
1,6-hexanediol.
BACKGROUND ART
[0002] 1,6-hexanediol is a useful substance used as a raw material
of polyester resins, urethane foam, urethane paint and adhesives.
For example, it can be used directly as a chain extender when used
as the raw material of polyurethanes, or can be used as a soft
segment by using in the production of polycarbonate diols and
polyester polyoles.
[0003] Although cyclohexanone and/or cyclohexanol, which are useful
as raw materials in the synthesis of .epsilon.-caprolactam, are
produced industrially by aerobic oxidation of cyclohexane,
1,6-hexandiol is produced by esterifying a mixture of carboxylic
acids, including glutaric acid, adipic acid, 6-hydroxycaproic acid
and so on produced as by-products during aerobic oxidation of
cyclohexane, with alcohol followed by hydrogenation to obtain
1,6-hexanediol that is separated by distillation (Patent Documents
1 and 2).
[0004] Since the 1,6-hexanediol obtained by the aforementioned
method contains impurities such as 1,4-cyclohexanediol,
1,5-hexanediol, 1,2-cyclohexanediol, 1,7-pentanediol,
1,5-pentanediol and high boiling point components, if, for example,
a polycarbonate diol is produced using 1,6-hexanediol for the raw
material, and this is then used as a raw material to carry out a
urethanation reaction, it was found that the polymerization rate is
slow, an adequate molecular weight cannot be obtained, and that
similar problems occur even in the case of using directly as a
chain extender in a urethanation reaction. In addition, there was
also the problem of similar effects appearing on the polymerization
rate during polyester production as well.
[0005] With respect to removal of the impurity,
1,4-cyclohexanediol, Patent Document 3 describes a method for
converting the aforementioned mixture of carboxylic acids to
cyclohexanone and cyclohexanol by preliminary hydrogenation
following esterification of the carboxylic acid mixture with an
alcohol, while Patent Document 4 describes a method for obtaining
an ester essentially free of 1,4-cyclohexanediol by
distillation.
[0006] However, the method employing preliminary hydrogenation had
the problem of inadequate product purity. In addition, although in
the method involving ester distillation it is preferable in that
the esters are monomers, in actuality, many of the active
ingredients of the carboxylic acid mixture become oligomer esters
as a result of concentration following extraction with water,
thereby requiring not only esterification of the carboxylic acid
monomers but also depolymerization of the oligomer esters in order
to obtain 1,6-hexanediol at high yield and high purity. However, in
the production processes of the prior art, since esterification of
carboxylic acid monomers and depolymerization of oligomer esters
are carried out simultaneously, Lewis acid catalysts and basic
catalysts effective in depolymerization are deactivated by the
water formed by esterification of carboxylic acids and residual
carboxylic acids, thereby resulting in the problem of considerable
time being required for depolymerization and the problem of
corrosion of the reaction vessel by water, carboxylic acids and
acid catalysts (such as mineral acids). In addition, although
esterification and depolymerization are equilibrium reactions,
there was also the problem in being unable to increase the
equilibrium reaction yield due to the effects of the water formed.
Moreover, considerable equipment was required to separate the
esters, water, alcohols and other components formed as a result of
esterification.
[0007] [Patent Document 1] U.S. Pat. No. 3,524,892
[0008] [Patent Document 2] U.S. Pat. No. 3,268,588
[0009] [Patent Document 3] Japanese Unexamined Patent Publication
No. S51-108040
[0010] [Patent Document 4] Japanese Unexamined International
Publication No. 2000-505468
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0011] As a result of conducting extensive studies for the purpose
of providing a process for synthesizing 1,6-hexanediol without the
aforementioned problems, the inventors of the present invention
found that the aforementioned problems are solved by process for
producing 1,6-hexanediol from cyclohexane, wherein together with
esterifying a carboxylic acid mixture obtained as a by-product of
oxidation of cyclohexane, a step in which carboxylic acid esters,
water and excess lower alcohols used for esterification are removed
from the reaction mixture by distillation is carried out
simultaneously, while carrying out a step in which oligomers
contained in the bottom liquid are converted to carboxylic acid
esters by depolymerization at high temperature and under high
pressure in the presence of a catalyst, and that highly pure
1,6-hexanediol can be obtained at high yield in which the contents
of impurities such as 1,4-cyclohexanediol, 1,5-hexanediol,
1,2-cyclohexanediol, 1,7-pentanediol, 1,5-pentanediol and high
boiling point components have been significantly reduced, thereby
leading to completion of the present invention.
Means for Solving the Problems
[0012] The present invention relates to a process for producing
1,6-hexanediol from cyclohexane, comprising the steps of:
[0013] (1) treating an aqueous extraction concentrate of a reaction
mixture obtained by oxidation of cyclohexane with a lower alcohol
to esterify monocarboxylic acids and dicarboxylic acids contained
in the extract, and simultaneously remove and separate by
distillation water, excess lower alcohols and carboxylic acid
esters;
[0014] (2) converting oligomer esters contained in the bottom
liquid to carboxylic acid esters by depolymerizing the oligomer
esters at a high temperature and high pressure in the presence of a
lower alcohol and a catalyst; and,
[0015] (3) hydrogenating the carboxylic acid esters distilled off
in the step (1) and the carboxylic acid esters obtained in the step
(2) either respectively or collectively to convert to
1,6-hexanediol.
EFFECTS OF THE INVENTION
[0016] As a result of using the process of the present invention,
esterification can be carried out efficiently and with fewer
equipment than in the prior art by esterifying while also removing
water and organic acids, and in the depolymerization step as well,
the reaction rate can be significantly improved without causing
deactivation of Lewis acid catalysts and basic catalysts
susceptible to the effects of water and acid while also making it
possible to inhibit corrosion of the reaction vessel. Moreover,
highly pure 1,6-hexanediol can be obtained at good yield in which
the contents of impurities that cause a decrease in the
polymerization rate during production of polyurethane or polyester,
such as 1,4-cyclohexanediol, 1,2-cyclohexanediol and
1,5-hexanediol, are significantly reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows an example of an esterification apparatus of
the process of the present invention;
[0018] FIG. 2 shows an example of an esterification apparatus of
the process of the present invention;
[0019] FIG. 3 is a phase change diagram of a depolymerization
reaction of the process of the present invention;
[0020] FIG. 4 is a drawing of an esterification apparatus of the
process of the present invention;
[0021] FIG. 5 is an example of a schematic flow chart of the
process of the present invention; and,
[0022] FIG. 6 shows graphs indicating the effects of reaction
temperature and reaction pressure on the yield of depolymerization
in a depolymerization step.
BEST MODE FOR CARRYING OUT THE INVENTION
[0023] The present invention produces 1,6-hexanediol from
cyclohexane by:
[0024] (1) carrying out a step in which a reaction mixture obtained
by oxidizing cyclohexane with oxygen or an oxygen-containing gas is
extracted with water to extract a carboxylic acid mixture
containing by-products such as glutaric acid, adipic acid and
6-hydroxycaproic acid, and then the extract is concentrated to have
a concentrate which is then treated with a lower alcohol to
esterify the monocarboxylic acids and dicarboxylic acids contained
in the concentrate, simultaneously with removing and separating by
distillation water, excess lower alcohols and carboxylic acid
esters;
[0025] (2) converting oligomer esters contained in the bottom
liquid to carboxylic acid esters such as glutaric acid ester,
adipic acid ester or 6-hydroxycaproic acid ester by depolymerizing
the oligomer esters at a high temperature and high pressure in the
presence of a lower alcohol and a catalyst, and
[0026] (3) hydrogenating the carboxylic acid esters distilled off
in the step (1) and the carboxylic acid esters obtained in the step
(2) either respectively or collectively to convert to
1,6-hexanediol.
[0027] The following provides a detailed explanation of the process
of the present invention.
[0028] In the step (1) of the present invention, a reaction mixture
obtained by oxidation of cyclohexane is extracted with water
followed by treatment of the concentrated extract with a lower
alcohol. As a specific means of obtaining the extract, first the
cyclohexane is oxidized with oxygen or an oxygen-containing gas to
obtain a mixture containing the main components of cyclohexanone
and cyclohexanol and by-products such as glutaric acid, adipic acid
and 6-hydroxycaproic acid. Although the method for oxidizing the
cyclohexane with oxygen or an oxygen-containing gas can be suitably
selected by a person with ordinary skill in the art, an example of
such a method is described in Ullmann's Encyclopedia of Industrial
Chemistry, 5th edition, 1987, Vol. A8, S.2/9. More specifically,
oxygen or an oxygen-containing gas is introduced in a reaction
vessel containing cyclohexane followed by using a cobalt or other
metal salt (such as cobalt octylate) as a catalyst and carrying out
the reaction at a temperature of 150 to 180.degree. C. under a
pressure of 0.8 to 1.2 MPa.
[0029] Next, by treating the resulting oxidized reaction mixture
with water, the carboxylic acid mixture is extracted into an
aqueous phase followed by separation from the cyclohexanone and
cyclohexanol. During the extraction, extraction can be carried out
using for example, 1 to 10% by weight of water with respect to the
oxidized reaction mixture.
[0030] At this stage, the extracted aqueous phase typically
contains 1 to 4% by weight of adipic acid, 1 to 4% by weight of
6-hydroxycaproic acid, 0.01 to 1% by weight of glutaric acid, 0.01
to 1% by weight of 5-hydroxyvaleric acid, 0.01 to 0.5% by weight of
1,2-cyclohexanediol (both cis and trans forms), 0.01 to 0.5% by
weight of 1,4-cyclohexanediol (both cis and trans forms), 0.01 to
1% by weight of formic acid, and numerous other mono- and
dicarboxylic acids, esters, alcohols, aldehydes and so forth having
individual contents of typically not exceeding 0.5% by weight.
Examples of other mono- and dicarboxylic acids, esters, alcohols,
aldehydes and other oxygen-containing compounds include acetic
acid, propionic acid, butyric acid, valeric acid, caproic acid,
oxalic acid, malonic acid, succinic acid, 4-hydroxybutyric acid and
.gamma.-butyrolactone.
[0031] Next, the aqueous layer containing the carboxylic acid
mixture is concentrated. Concentration is normally carried out by
distillation. As a result of distilling at a temperature of 10 to
250.degree. C., preferably 20 to 200.degree. C. and more preferably
30 to 200.degree. C. and at a pressure of 0.1 to 150 KPa,
preferably 2 to 110 KPa, and more preferably 10 to 105 KPa, the
aqueous layer is concentrated by 1/50 to 1/2 times and preferably
1/20 to 1/3 times the amount prior to concentration. As a result of
concentrating under these conditions, the water can be concentrated
to 2% by weight or less and preferably 1% by weight or less of the
total amount.
[0032] In this concentration, various carboxylic acids contained in
the extracted aqueous layer are partially condensed to form
oligomer esters.
[0033] Simultaneously with the treatment with an a lower alcohol of
the carboxylic acid mixture (COA), which is obtained after
extraction with water and concentration as above, to esterify the
monocarboxylic acids and dicarboxylic acids contained in the
concentrated extract, a step in which water, excess lower alcohol
and carboxylic acid esters are removed and separated by
distillation is carried out at the same time. These esterification
and distillation and separation steps can be carried out in a
single apparatus.
[0034] Examples of the lower alcohol used for esterification
include methanol and ethanol, with methanol being used
preferably.
[0035] In addition, the amount of the lower alcohol used is such
that the mixing ratio (weight ratio) with respect to the
aforementioned concentrated carboxylic acid mixture (COA) is 0.1 to
30, advantageously 0.5 to 15 and particularly advantageously 1 to
5.
[0036] During the esterification, the concentrated carboxylic acid
mixture (COA) described above is dropped into the upper or
intermediate portion of a reaction apparatus in a reaction vessel
such as a stirring tank, bubble tower or distillation tower, a
plurality of which may be used as necessary, and esterification is
carried out by introducing the lower alcohol from the bottom of the
reaction apparatus and allowing to react by co-flow, or by
introducing a gas of the lower alcohol into a liquid phase of the
aforementioned concentrated carboxylic acid mixture (COA), or by
using a combination thereof. This reaction is normally carried out
by heating, and a catalyst is used as necessary.
[0037] The lower alcohol can be introduced into the system as a
liquid and then converted to a gas, or it can be introduced into
the system after been gasified outside the system.
[0038] In the esterification comprised of introducing a lower
alcohol into the liquid phase of the aforementioned concentrated
carboxylic acid mixture (COA), the liquid phase can be stirred with
a stirrer. In addition, a distillation column can be provided for
the distillate gas to separate undesirable high boiling point
components that have contaminated the esters.
[0039] Although the heating temperature can be suitably selected
according to the type of lower alcohol used, the reaction can be
carried out at a temperature of, for example, 50 to 400.degree. C.,
preferably 100 to 300.degree. C. and more preferably 150 to
250.degree. C.
[0040] In addition, although the esterification step can be carried
out under pressurized conditions, it can also be carried out at the
pressure within the reaction apparatus used for the esterification
reaction. Esterification is preferably carried out at a pressure of
0 to 5 MPa, more preferably 0.5 to 2 MPa and particularly
preferably 1 to 1.5 MPa.
[0041] The reaction conditions regarding the aforementioned
temperature and pressure can be suitably selected according to the
type of lower alcohol used for esterification. In the case of using
methanol, for example, a temperature of 100 to 300.degree. C.
(preferably 240.degree. C.) and a pressure of 0.01 to 10 MPa
(preferably 0.5 to 2 MPa) can be used.
[0042] Although the reaction time of the esterification step can be
suitably selected according to the type of lower alcohol used,
amount of the reaction compound and so forth, it can be made to be,
for example, 0.3 to 10 hours and preferably 0.5 to 5 hours.
[0043] Although the esterification step can be carried out without
adding a catalyst, it can also be carried out in the presence of a
catalyst to increase the reaction rate. Homogeneously dissolving
catalysts or solid catalysts can be used for the catalyst. Examples
of homogeneously dissolving catalysts include mineral acids (such
as sulfuric acid, phosphoric acid or hydrochloric acid), sulfonic
acids (such as p-toluene sulfonic acid), heteropoly acids (such as
phosphotungstenic acid), and Lewis acids (but only water-resistance
and acid-resistant Lewis acids).
[0044] Acidic or hyperacidic materials can be used for the solid
catalyst. The examples include acidic or hyperacidic metal oxides;
SiO.sub.2, Al.sub.2O.sub.3, SnO.sub.2, ZrO.sub.2, layered silicates
or zeolite to which mineral acid group such as sulfate groups or
phosphate groups have been added to increase acidity; and, ion
exchange resins having sulfonic acid groups or carboxylic acid
groups.
[0045] The solid catalyst can be used in the form of a fixed bed or
a suspended bed.
[0046] In the case of a suspended bed, the amount of catalyst used
is 0.1 to 5% by weight with respect to the total amount, and in the
case of a fixed bed, the LHSV is within the range of 0.1 to 5
h.sup.-1.
[0047] The amount used of homogeneously dissolving catalysts or
solid catalysts is 0.01 to 1% by weight with respect to the total
amount. Although the catalyst can be separated after the
esterification step, it can also be used as a catalyst of the
subsequent depolymerization step.
[0048] The following provides a more detailed explanation of the
aforementioned esterification step. The esterification step can be
carried out by, for example, a gas-liquid reaction in which a
gaseous lower alcohol is introduced into a carboxylic acid mixture
in a reaction apparatus (FIG. 1), or by a gas-liquid reaction in
which a carboxylic acid mixture (COA) is dropped in from the upper
or intermediate portion of a reaction distillation column such as a
packed tower or tray tower and a gaseous lower alcohol is
introduced from the bottom (FIG. 2). As a result of employing such
a procedure, in addition to the esterification proceeding as a
result of the alcohol dissolving in the liquid phase, the water
formed in the liquid phase is released in the vapor phase, thereby
allowing the water to be adequately removed from the system and
being able to efficiently achieve a low acid value (AV) of 30
mgKOH/g or less. In addition, the amounts of unreacted high boiling
point components, such as adipic acid, 6-hydroxycaproic acid or
1,4-cyclohexanediol, in the carboxylic acid mixture, and a catalyst
in the case of using a catalyst, mixed into the distillate are
negligible and do not present a problem. Namely, the esterification
step is characterized by the esterification reaction and
distillation separation of undesirable substances being able to be
carried out simultaneously.
[0049] The mixture of carboxylic acid esters, lower alcohol and
water separated in the esterification step is introduced into a
distillation column where the lower alcohol is distilled off at a
pressure of 0.1 to 200 KPa and temperature of 0 to 150.degree. C.,
and preferably a pressure of 10 to 150 KPa and temperature of 25 to
200.degree. C. The resulting bottom liquid is either re-introduced
into the distillation column or introduced into a second
distillation column where the water is distilled off at a pressure
of 0.1 to 150 KPa and temperature of 0 to 150.degree. C., and
preferably a pressure of 4 to 120 KPa and temperature of 25 to
120.degree. C. The carboxylic acid esters separated from the
aforementioned mixture in this manner can be further distilled
prior to supplying to the subsequent hydrogenation step (3).
[0050] On the other hand, those compounds contained in the
concentrated carboxylic acid mixture that have formed dimers with
terminal hydroxyl groups of 6-hydroxycaproic acid and oligomer
esters (referred to as oligomers) remain in the form of bottom
liquid.
[0051] In step (2) of the present invention, oligomer esters
contained in the bottom liquid after the water and carboxylic acid
esters formed in step (1) and excess lower alcohol are distilled
off, followed by distillative separation, are depolymerized at a
high temperature and high pressure in the presence of a catalyst
and lower alcohol to convert to carboxylic acid esters such as
adipic acid ester and 6-hydroxycaproic acid ester.
[0052] Examples of catalysts that can be used in step (2) include
homogeneously dissolving catalysts and solid catalysts. Although
examples of homogeneously dissolving catalysts include mineral
acids (such as sulfuric acid, phosphoric acid or hydrochloric
acid), sulfonic acids (such as p-toluene sulfonic acid), heteropoly
acids (such as phosphotungstenic acid), Lewis acids (such as
aluminum compounds, vanadium compounds, titanium compounds, boron
compounds or zinc compounds), and basic catalysts (such as oxides,
carbonates, hydroxides, alcolates or amines of alkaline metals or
alkaline earth metals), Lewis acids or basic catalysts are used
preferably, while Lewis acids are used more preferably.
[0053] Examples of preferable Lewis acids include
tetraalkoxytitanium, and more preferably tetra-n-butoxytitanium and
tetraisopropoxytitanium.
[0054] In the process of the present invention, water formed by the
esterification reaction and residual carboxylic acids are removed
from the system in step (1), and deterioration of the
aforementioned catalysts by acid and water is reduced in step (2),
and therefore a Lewis acid can be used particularly preferably.
[0055] The amount of homogeneously dissolving catalyst used is
typically 0.00001 to 0.01 and advantageously 0.0001 to 0.005 as the
weight ratio with respect to the bottom liquid of step (1).
[0056] An acidic catalyst or hyperacidic catalyst can be used for
the solid catalyst, examples of which include acidic or hyperacidic
metal oxides; SiO.sub.2, Al.sub.2O.sub.3, SnO.sub.2, ZrO.sub.2,
layered silicates or zeolite to which mineral acid groups such as
sulfate groups or phosphate groups and so forth have been added to
increase acidity; and, ion exchange resins having sulfonic acid
groups or carboxylic acid groups. The solid catalyst can be used in
the form of a fixed bed or a suspended bed.
[0057] In the case of using a homogeneously dissolving acid
catalyst for the catalyst, the reaction liquid may be neutralized
with base following depolymerization. The amount of base used is 1
to 1.5 equivalents per acid equivalent of the catalyst. Typical
examples of the base include oxides, carbonates, hydroxides,
alcolates or amines of alkaline metals or alkaline earth metals.
These can be used directly or they can be used after dissolving in
the lower alcohol used for depolymerization.
[0058] Examples of lower alcohols that can be used in step (2)
include methanol and ethanol, and methanol can be used
preferably.
[0059] The amount of lower alcohol that can be used for
depolymerization is 0.5 to 10 times (weight) and preferably 1 to 5
times the amount of distillation bottom liquid in step (1)
containing oligomer esters.
[0060] The depolymerization reaction is carried out at a high
temperature and high pressure, and more specifically, at a high
temperature and a pressure higher than the vapor pressure curve of
the depolymerization reaction liquid (liquid phase). More
specifically, in the case of using methanol for the lower alcohol,
the reaction is carried out in the liquid phase under conditions of
200.degree. C. and 4 MPa or higher, preferably 240.degree. C. and 8
MPa or higher, particularly preferably 250 to 280.degree. C. and 9
to 15 MPa, and more preferably 265 to 275.degree. C. and 9 to 12
MPa.
[0061] An example of a vapor pressure curve indicating the phase
change of the depolymerization reaction liquid in the case of
changing the methanol/ester ratio using methanol for the lower
alcohol is shown in FIG. 3.
[0062] Furthermore, this vapor pressure curve can be obtained by
reducing the pressure in an autoclave equipped with an
approximately 50 cc sapphire glass (visible apparatus), followed by
charging 1/3 the volume of the bottom liquid after the
esterification of step (1) and lower alcohol, and raising the
temperature with the reaction vessel sealed while plotting the
relationship between temperature and pressure. As a result of using
conditions above this vapor pressure curve, namely using conditions
such that the pressure is increased to a pressure above the vapor
pressure curve (gas-liquid state), a uniform liquid phase results
and the depolymerization reaction proceeds under these
conditions.
[0063] Since the depolymerization reaction proceeds rapidly as a
result of carrying out the depolymerization reaction in the liquid
phase under the high temperature and high pressure as described
above, the reaction time can be made to be 0.5 to 10 minutes and
preferably 1 to 5 minutes. In addition, since the reaction is in a
uniform phase, the scale of the reaction can be increased
easily.
[0064] In specifically carrying out the depolymerization reaction,
a lower alcohol and catalyst are added to the bottom liquid in step
(1) followed by heating under pressure under the aforementioned
conditions.
[0065] Since water formed by the esterification in the
aforementioned step (1) is removed from the system and the acid
value (AV) decreases, corrosion of the reaction vessel by acid and
moisture is reduced.
[0066] Next, the excess lower alcohol used is removed by
distillation from the reaction mixture after depolymerization. The
pressure at that time is 0.1 to 150 KPa, preferably 2 to 100 KPa,
and particularly preferably 4 to 80 KPa. The temperature at the top
of the column is, for example, 0 to 150.degree. C., preferably 15
to 90.degree. C. and particularly preferably 25 to 75.degree. C.
The temperature at the bottom of the column is 70 to 250.degree.
C., advantageously 80 to 220.degree. C. and particularly
advantageously 100 to 200.degree. C.
[0067] Furthermore, flash distillation, in which the pressure is
released based on the depolymerization conditions, is preferably
used for removal of excess lower alcohol.
[0068] As a result of distilling under these conditions, excess
lower alcohol, water and low boiling point esters corresponding to,
for example, formic acid, acetic acid and propionic acid, contained
in the reaction mixture after depolymerization are separated. This
matter flow can either be burned off or the recovered alcohol can
be further reused in the esterification step or depolymerization
step.
[0069] Separate from the aforementioned lower alcohol, water and
low boiling point esters corresponding to, for example, formic
acid, acetic acid and propionic acid, a mixture primarily
containing carboxylic acid esters of the lower alcohol used and
dicarboxylic acids such as adipic acid, glutaric acid and
hydroxycarboxylic acids (such as 6-hydroxycaproic acid and
5-hydroxyvaleric acid), unreacted oligomer esters, free or
esterified 1,4-cyclohexanediol and other high boiling point
components is also separated.
[0070] This mixture is preferably applied to distillation prior to
the hydrogenation of the subsequent step (3) to remove high boiling
point components such as 1,4-cyclohexanediol and AV components that
are poisonous to the hydrogenation catalyst (monocarboxylic acids
and dicarboxylic acids contained in step (1) such as adipic acid,
glutaric acid, 6-hydroxycaproic acid, 5-hydroxyvaleric acid and
condensates thereof). This distillation may be carried out
separately or in combination with distillation of the carboxylic
acid esters separated by distillation together with water and
alcohol following esterification in the previous step (1).
[0071] The pressure of this (ester) distillation step is 0.1 to 100
KPa, advantageously 0.1 to 10 KPa and particularly advantageously
0.3 to 5 KPa. The temperature at the top of the column is 50 to
200.degree. C., advantageously 80 to 180.degree. C. and
particularly advantageously 90 to 150.degree. C. The temperature at
the bottom of the column is 70 to 250.degree. C., advantageously
100 to 230.degree. C. and particularly advantageously 130 to
220.degree. C.
[0072] In addition, the bottom liquid obtained as a result of the
aforementioned distillation can also be re-applied to
depolymerization under the same conditions as described above to
convert the oligomer esters contained in the bottom liquid to
carboxylic acid esters. Since water is removed from the system in
the aforementioned step (1), even in the case of having used a
Lewis acid in the first round of depolymerization of step (2),
since the Lewis acid is not subjected to deactivation by water, the
Lewis acid may not again be added to this second depolymerization
reaction. In this manner, the carboxylic acid esters obtained from
the second round of depolymerization can be applied to the
hydrogenation of the subsequent step (3) either separately or
together with the previously obtained carboxylic acid ester to
obtain 1,6-hexanediol.
[0073] In step (3) of the present invention, the carboxylic acid
esters separated by distillation in the aforementioned step (1) and
the carboxylic acid esters obtained in the aforementioned step (2)
are hydrogenated followed by distillation to convert to
1,6-hexanediol.
[0074] The carboxylic acid esters separated by distillation in the
aforementioned step (1) and the carboxylic acid esters
depolymerized in the aforementioned step (2), and further applied
to distillation depending on the case, can be hydrogenated
separately or together. Hydrogenation reduction is carried out
catalytically in the hydrogen gas phase or liquid phase using a
catalyst.
[0075] All homogeneous or heterogeneous catalysts suitable for
hydrogenation of carbonyl groups can be used for the hydrogenation
catalyst, examples of which include metals, metal hydroxides, metal
compounds and mixtures thereof.
[0076] Here, examples of homogeneous catalysts include those
described in Houben-Weyl, Methoden der Organischen Chemie, Band
IV/1c, GeorgThieme, Verlag Stuttgart, 1980.S.4567. In addition,
examples of heterogeneous catalysts include those described in
Houben-Weyl, Methoden der Organischen Chemie, Band IV/1c, S.16-26.
Examples of metal catalysts that can be used include metals of
subgroups I and VI to VIII of the periodic table described in the
aforementioned non-patent document, and particularly copper,
chromium, molybdenum, manganese, rhenium, ruthenium, cobalt, nickel
and palladium, and one type or a plurality of types of these metals
can be used.
[0077] Copper-containing hydrogenation catalysts can be used
particularly preferably, specific examples of which include Cu--Cr,
Cu--Zn, Cu--Zn--Al, Cu--Zn--Ti, Cu--Fe--Al and Cu--Si. In addition,
there are no particularly limitations on the form of these
catalysts, and may be suitably selected from forms such as a
powder, granules or tablets according to the shape of the reaction
vessel. In the case of a copper-zinc catalyst, a trace amount of
aluminum, magnesium or zirconium and so forth may be contained.
[0078] A heterogeneous catalyst is used in the form of a fixed bed
or suspended bed in the hydrogenation reaction.
[0079] Although the amount of catalyst can be suitably selected
according to the type of catalyst, the LHSV is typically 0.1 to 5
h.sup.-1 in the case of a fixed bed, while in the case of a
suspended bed, the amount used can be 0.1 to 5% by weight with
respect to the suspended bed.
[0080] In the case of carrying out the hydrogenation reaction in a
gaseous phase, a fixed bed catalyst is used and the pressure is 0.1
to 15 MPa, preferably 0.5 to 12 MPa and more preferably 1 to 10
MPa.
[0081] The reaction temperature is 100 to 350.degree. C. and
preferably 120 to 300.degree. C.
[0082] In the case of carrying out the hydrogenation reaction in
the liquid phase, a fixed bed or a suspended bed can be used, and
in either case the pressure is 1 to 35 MPa and the temperature is
100 to 350.degree. C., and preferably 5 to 30 MPa and 200 to
300.degree. C.
[0083] Hydrogenation reduction can be carried out in a single
reaction vessel or can be carried out by connecting a plurality of
reaction vessels in series. Although hydrogenation reduction can
also be carried out discontinuously, it is preferably carried out
continuously.
[0084] The reaction mixture obtained by carrying out hydrogenation
reduction under the conditions described above primarily contains
1,6-hexanediol, while other components in the form of
1,5-pentanediol, 1,4-butanediol, 1,2-cyclohexanediol, small amounts
of mono- or dialcohols having 1 to 7 carbon atoms and water are
also obtained.
[0085] This reaction mixture can be separated by applying to a
membrane system or distillation column into water and low boiling
point components such as lower alcohols, and components primarily
including 1,5-pentanediol, 1,2-cyclohexanediol and 1,6-hexanediol.
The pressure during this distillation is 1 to 150 KPa, preferably
10 to 120 KPa and more preferably 20 to 110 KPa. The distillation
temperatures are such that the temperature at the top of the column
is 0 to 100.degree. C. and preferably 30 to 70.degree. C., while
the temperature at the bottom of the column is 100 to 220.degree.
C. and preferably 120 to 200.degree. C.
[0086] The component primarily containing 1,6-hexanediol obtained
by the aforementioned distillative separation can be further
purified in a distillation column to separate the 1,6-hexanediol
from the 1,5-pentanediol, and 1,2-cyclohexanediol, and low boiling
point compounds which may be present depending on the case. These
distillation conditions can be adjusted to a pressure of, for
example, 0.1 to 100 KPa, preferably 0.5 to 50 KPa and more
preferably 1 to 10 KPa, a temperature at the top of the
distillation column of, for example, 50 to 200.degree. C. and
preferably 60 to 200.degree. C., and a temperature at the bottom of
the distillation column of 130 to 250.degree. C. and preferably 150
to 220.degree. C. As a result of carrying distillative purification
using a distillation column under such conditions, 1,6-hexanediol
can be obtained at a purity of 99% or more.
[0087] In addition, in the case of desiring to acquire
1,5-pentanediol, this can be further separated with a distillation
column.
EXAMPLE 1
[0088] The following provides a more detailed explanation of the
present invention through examples thereof.
[0089] Step 1: Oxidation of Cyclohexane and Extraction with
Water
[0090] Cyclohexane was oxidized under conditions of 160.degree. C.
and 1 MPa and then extracted using water under conditions of
160.degree. C. and 1 MPa to obtain a carboxylic acid mixture having
the composition indicated below.
Aqueous extract of cyclohexane oxide
[0091] (Composition of Aqueous Extract)
[0092] Valeric acid: 0.1% by weight
[0093] 5-hydroxyvaleric acid: 0.11% by weight
[0094] Caproic acid: 0.02% by weight
[0095] Succinic acid: 0.3% by weight
[0096] 6-hydroxycaproic acid: 3.8% by weight
[0097] Glutaric acid: 0.3% by weight
[0098] Adipic acid: 2.7% by weight
[0099] 1,2-cyclohexanediol: 0.02% by weight
[0100] 1,4-cyclohexanediol: 0.04% by weight
[0101] Other: Water and trace components
[0102] Step 2: Concentration of Aqueous Extract
[0103] Next, the subject extract was concentrated under conditions
of 13 KPa to obtain a concentrate having the composition indicated
below.
[0104] (Composition)
[0105] Oxycaproic acid: 27.9% by weight (of which about 90% by
weight was oligomers)
[0106] Adipic acid: 19.8% by weight (of which about 50% by weight
was oligomers)
[0107] H.sub.2O: 2.0% by weight
[0108] 1,4-cyclohexanediol: 0.7% by weight
[0109] Step 3: Esterification
[0110] The bottom liquid (aforementioned concentrate) obtained in
step 2 was continuously fed into a reaction apparatus (gas-liquid
reaction tank, 700 cc.times.2 tanks, FIG. 4) at the rate of 700 g/h
and the methanol was gasified followed by bubbling into the
reaction liquid of the two tanks at 350 g/h, respectively. At that
time, the temperature within the reaction tanks was maintained at
240.degree. C. by external heating, and the pressure was adjusted
with a back pressure regulating value so as to keep the distillate
gas at 1 MPa. As a result, a distillate gas and bottom liquid were
respectively obtained as indicated below.
[0111] Distillate Gas (after cooling and condensation): 757 g/h
[0112] H.sub.2O: 6.9% by weight [0113] Dimethyl adipate: 8.7% by
weight [0114] Methyl hydroxycaproate: 1.7% by weight [0115]
1,4-cyclohexanediol: Trace amount [0116] Adipic acid: Trace amount
[0117] 6-hydroxycaproic acid: Trace amount [0118] Other: MeOH, low
boiling point components
[0119] Bottom Liquid: 643 g/h [0120] Acid value (AV)=20 mgKOH/g
[0121] H.sub.2O: 0.1% by weight [0122] Other: Adipic acid,
hydroxycaproic acid and other oligomer components
[0123] Step 4: Recovery of Methanol and Distillative Removal of
Water
[0124] The distillate gas obtained as previously described was
cooled and condensed followed by recovering the methanol with a
first column according to the conditions indicated below and
removing H.sub.2O and low boiling point components with a second
column.
[0125] First Column: [0126] Distillation apparatus: Sulzer Labo
Packing EX (Sumitomo Heavy Industries), 5 units [0127] Distillation
conditions: 0.1 kg/cm.sup.2G, column top: 66.degree. C., column
bottom: 111.degree. C.
[0128] Second Column: [0129] Distillation apparatus: Sulzer Labo
Packing EX (Sumitomo Heavy Industries), 5 units [0130] Distillation
conditions: 410 Torr, column top: 76.degree. C., column bottom:
190.degree. C.
[0131] As a result, a concentrate was obtained having the
composition indicated below.
[0132] MeOH: 0.2% by weight
[0133] Dimethyl adipate: 74.2% by weight
[0134] Methyl hydroxycaproate: 14.6% by weight
[0135] H.sub.2O: 0.1% by weight
[0136] Caprolactone: 0.8% by weight
[0137] 1,4-cyclohexanediol (cis+trans): ND
[0138] Dimethyl glutarate: 3.7% by weight
[0139] Dimethyl succinate: 1.2% by weight
[0140] A study was made of comparative examples (esterification and
concentrate in the absence of bubbling) with respect to the
aforementioned example.
[0141] An esterification reaction was carried out by charging 6 kg
of a carboxylic acid mixture (COA) and 3.9 kg of MeOH into a 20 L
autoclave. The essentially reached equilibrium in 3 hours at
240.degree. C. and 3 MPa, and the analytical values of the reaction
liquid at that time consisted of an acid value (AV) of 42 mgKOH/g
and an H.sub.2O content of 8.5% by weight.
[0142] This liquid was then concentrated using a 10 L evaporator at
30 to 250 Torr and oil bath temperature of 50 to 100.degree. C. to
obtain 5940 g of a concentrate having the composition indicated
below.
[0143] MeOH: 0.2% by weight
[0144] Dimethyl adipate: 13.6% by weight (yield based on COA:
57%)
[0145] Methyl 6-hydroxycaproate: 16.0% by weight (yield based on
COA: 55%)
[0146] H.sub.2O: 0.1% by weight
[0147] Step 5: Depolymerization
[0148] The bottom liquid obtained in step 3 at 100 g/h, methanol at
200 g/h and tetrabutoxytitanium catalyst at 0.1 g/h were
continuously fed into a tubular reactor followed by carrying out a
depolymerization reaction under the conditions indicated below.
[0149] Reactor conditions: 270.degree. C., 10 MPa, residence time:
5 minutes
[0150] The yield of dimethyl adipate and methyl 6-hydroxycaproate
was 83%.
[0151] Step 6: Removal of Methanol
[0152] The reaction liquid obtained as a result of the
depolymerization of step 5 was distilled under the conditions
indicated below to remove the methanol and low boiling point
fraction.
[0153] Distillation apparatus: Sulzer Labo Packing (5 units)
[0154] Distillation conditions: 160 Torr, column top: 34.degree.
C., column bottom: 89.degree. C.
[0155] Step 7: Purification of Ester
[0156] The bottom liquid obtained in steps 4 and 6 was distilled
under the conditions indicated below to obtain dimethyl adipate and
methyl oxycaproate.
[0157] Distillation apparatus: Sulzer Labo Packing (27 units)
[0158] Distillation conditions: 5 Torr, column top: 70 to
111.degree. C., column bottom: 117 to 188.degree. C., reflux ratio:
10
[0159] Step 8: Hydrogenation
[0160] The esters obtained in step 7 underwent a hydrogenation
reaction in a solid-liquid reaction tank under the conditions
indicated below.
[0161] Hydrogenation apparatus: Suspended bed
[0162] Hydrogenation conditions: 250.degree. C., 25 MPa, catalyst:
CuO--ZnO catalyst (copper/zinc (metal weight ratio)=1/1): 1% by
weight, 5 hours
[0163] Result: Saponification value conversion rate: 98%
[0164] Step 9: Purification of Diol
[0165] 1000 g of the reaction liquid obtained in step 8 was
purified by distillation under the conditions indicated below to
obtain highly pure 1,6-hexanediol.
[0166] Distillation apparatus: Sulzer Labo Packing (30 units),
reflux ratio: 10
[0167] Methanol main component: 257 g (760 Torr)
[0168] 1,5-pentanediol main component: 60 g
[0169] 1,6-hexanediol main component: 554 g (10 Torr, column top:
137 to 140.degree. C., column bottom: 150 to 190.degree. C.)
[0170] The composition of the impurities in the product fraction
present in the 1,6-hexandiol main component was as indicated
below.
[0171] 1,4-cyclohexanediol: 0.1% by weight
[0172] 1,2-cyclohexanediol: ND
[0173] 1,5-hexanediol: ND
[0174] 1,7-heptanediol: ND
[0175] 1,5-pentanediol: 0.1% by weight
[0176] Thus, the yield of 1,6-hexanediol was confirmed to be 90% or
more, and additionally confirmed to be in excess of 95%.
[0177] A schematic drawing of the aforementioned steps 1 to 9 is
shown in FIG. 5.
COMPARATIVE EXAMPLE 1
Example of Carrying Out Depolymerization Reaction without
Separating Oligomers
[0178] A carboxylic acid mixture (concentrate of step 2: COA) at
100 g/h and methanol at 200 g/h were continuously fed to a tubular
reactor under the conditions indicated below to obtain carboxylic
acid esters.
[0179] Reactor conditions: 270.degree. C., 10 MPa, residence time:
10 minutes
[0180] Reaction results: Yield of dimethyl adipate and methyl
6-hydroxycaproate: 35%
COMPARATIVE EXAMPLE 2
Example of Carrying Out Depolymerization Reaction without
Separating Oligomers
[0181] A carboxylic acid mixture (concentrate of step 2: COA) at
100 g/h, methanol at 200 g/h and tetraisopropoxytitanium catalyst
at 0.3 g/h were continuously fed to a tubular reactor under the
conditions indicated below to obtain carboxylic acid esters.
[0182] Reactor conditions: 270.degree. C., 10 MPa, residence time:
10 minutes
[0183] Reaction results: Yield of methyl adipate and methyl
6-hydroxycaproate: 40%
EXAMPLE 2
[0184] A study was made of the effect of water content on the acid
value (AV) of the resulting bottom liquid (reaction liquid) and
distillate gas by changing the amount of water in the methanol used
in the esterification step of Step 3 in Example 1. The study was
made under the conditions of a temperature of 200.degree. C. or
240.degree. C., pressure of 1.0 MPa, and 1:1 ratio of methanol to
carboxylic acid mixture. The results are shown in Table 1. The acid
values (AV) of both the bottom liquid and distillate gas tended to
increase as the water content in the methanol increased.
TABLE-US-00001 TABLE 1 Effect of Water Content in MeOH (Two-tank
gas-liquid stirring tank) Bottom liquid MeOH/ Liquid analytical
Distillate liquid Reaction H.sub.2O COA residence values analytical
values tank in MeOH Pressure Weight Temperature time AV H2O AV H2O
DMA MOC -- wt % MPa ratio .degree. C. h mgKOH/g wt % mgKOH/g wt %
wt % wt % 1st tank 0.1 1 1 200 1.2 94 1.1 3.8 11.9 2.8 0.8 1st tank
3.5 1 1 200 1.2 102 1.6 3.5 13.8 2.6 0.7 1st tank 5 1 1 200 1.2 104
1.7 4.4 16 2.7 0.7 2nd tank 0.1 1 1 240 0.7 23 0.1 2.9 3 7.6 2.8
2nd tank 1 1 1 240 0.7 25 0.2 2.9 4 7.4 2.6 2nd tank 3 1 1 240 0.7
33 0.4 3 5.5 7.3 2.5 Note: Liquid in which the AV value had
decreased to 100 mgKOH/g in the reaction of the first tank was fed
to the second tank.
EXAMPLE 3
[0185] A study was made of the effects on the acid values (AV) of
the resulting bottom liquid (reaction liquid) and distillate gas by
changing the reaction type to an one-tank system (FIG. 1), a
two-tank system (FIG. 4) and a reaction distillation system using a
reaction distillation column (FIG. 2) in the esterification step of
Step 3 in Example 1. The results are shown in Table 2. The best
acid values were demonstrated to be obtained with a two-tank
system.
TABLE-US-00002 TABLE 2 Effect of Reaction Type Bottom liquid Liquid
phase analytical Distillate liquid Reaction MeOH/COA residence
values analytical values type Pressure Weight Temperature time AV
H2O AV H2O DMA MOC -- MPa ratio .degree. C. h mgKOH/g wt % mgKOH/g
wt % wt % wt % One-tank type 1.5 1 240 2.2 45 1 6.1 14.2 4.9 1.6
Two-tank type 1.5 1 240 1.4 17 0.4 2.5 4.6 6.5 2.3 Reaction 1.5 1
240 0.7 22 0.4 34 21 1.9 0.6 distillation Note: DMA: Dimethyl
adipate, MOC: Methyl 6-hydroxycaproate
EXAMPLE 4
[0186] A study was made of the effects on the acid values (AV) of
the resulting bottom liquid (reaction liquid) and distillate liquid
by changing the residence times in the first and second tanks in
the esterification step of Step 3 in Example 1. The results are
shown in Table 3.
TABLE-US-00003 TABLE 3 Effects of Residence Time (Two-tank
gas-liquid stirring tank) Bottom liquid Liquid analytical
Distillate liquid Reaction MeOH/COA residence values analytical
values type Pressure Weight Temperature time AV H2O AV H2O DMA MOC
-- MPa ratio .degree. C. h mgKOH/g wt % mgKOH/g wt % wt % wt % 1st
tank 11 1 200 0.7 112 1.2 4.9 11 2.5 0.7 1st tank 11 1 200 1.2 94
1.1 3.8 11.9 2.8 0.8 1st tank 11 1 200 2.2 79 1.1 4.4 11.8 3 0.8
2nd tank 11 1 240 0.7 23 0.1 2.9 3 7.6 2.8 2nd tank 11 1 240 2.2 11
0.2 1.5 3.3 8.4 3 Note: Liquid in which the AV value had decreased
to 100 mgKOH/g in the reaction of the first tank was fed to the
second tank.
EXAMPLE 5
[0187] A study was made of the effects on the acid values (AV) of
the resulting bottom liquid (reaction liquid) and distillate gas by
changing the ratio of the methanol to the concentrated carboxylic
acid mixture (COA) esterified in the esterification step of Step 3
in Example 1. The results are shown in Table 4.
TABLE-US-00004 TABLE 4 Effects of MeOH/COA Ratio (Two-tank
gas-liquid stirring tank) Bottom liquid Liquid analytical
Distillate liquid Reaction MeOH/COA residence values analytical
values type Pressure Weight Temperature time AV H2O AV H2O DMA MOC
-- MPa ratio .degree. C. h mgKOH/g wt % mgKOH/g wt % wt % wt % 1st
tank 1 0.5 200 1.2 110 2 5 20.2 2.5 0.5 1st tank 1 1 200 1.2 94 1.1
3.8 11.9 2.8 0.8 1st tank 1 2 200 1.2 87 0.6 3.6 6.7 2.6 0.8 2nd
tank 1.5 0.5 240 0.7 17 0.4 2.5 4.6 6.5 2.3 2nd tank 1.5 1 240 0.7
12 0.2 1.3 2.9 6.2 2.6 2nd tank 1.5 2 240 0.7 7 0.1 1 1.4 5.2 2.9
Note: Liquid in which the AV value had decreased to 100 mgKOH/g in
the reaction of the first tank was fed to the second tank.
EXAMPLE 6
[0188] A study was made of the effects on precipitation of
tetrabutoxytitanium catalyst in the depolymerization reactor in the
depolymerization step of Step 5 in Example 1 by changing the acid
value (AV) of the concentrated carboxylic acid mixture
(COA)/methanol in the esterification step of Step 3 in Example 1.
There was demonstrated to be hardly any precipitation of
tetrabutoxytitanium catalyst when the acid value (AV) in the
concentrated carboxylic acid mixture (COA)/methanol was 30 mgKOH/g
or less. The results are shown in Table 6.
EXAMPLE 7
[0189] A study was made of the effects on the acid values (AV) of
the resulting bottom liquid (reaction liquid) and distillate liquid
by changing the reaction pressure in the esterification step of
Step 3 in Example 1. Those results are shown in Table 5.
TABLE-US-00005 TABLE 5 Effects of Pressure (Two-tank gas-liquid
stirring tank) Bottom liquid Liquid analytical Distillate liquid
Reaction MeOH/COA residence values analytical values type Pressure
Weight Temperature time AV H2O AV H2O DMA MOC -- MPa ratio .degree.
C. h mgKOH/g wt % mgKOH/g wt % wt % wt % 1st tank 0.2 1 240 1 362
0.1 18 5.3 0.1 0.17 1st tank 0.5 1 240 1 102 0.3 18 9.5 6 1.6 1st
tank 0.8 1 240 1 95 0.5 12 11 5.8 1.6 1st tank 1 1 240 1 76 0.6 11
12.2 5.9 1.9 1st tank 1.5 1 240 1 57 1 6.8 14 5.7 1.8 2nd tank 0.2
1 240 0.7 90 0.1 5 2 1.2 0.4 2nd tank 0.5 1 240 0.7 55 0.1 5 2.6 7
2.7 2nd tank 1 1 240 0.7 23 0.1 2.9 3 7.6 2.8 2nd tank 1.5 1 240
0.7 12 0.2 1.3 2.9 6.2 2.6 Note: Liquid in which the AV value had
decreased to 100 mgKOH/g in the reaction of the first tank was fed
to the second tank.
EXAMPLE 8
[0190] A study was made of the effects on yield by changing the
amount of tetrabutoxytitanium catalyst used for the bottom liquid
supplied for depolymerization in the depolymerization step of Step
5 in Example 1. The study was made under the conditions of using
twice the amount of methanol (weight ratio), a temperature of
270.degree. C. and a pressure of 11 MPa. The results are shown in
Table 6. Yield tended to increase as the amount of catalyst
increased.
EXAMPLE 9
[0191] A study was made of the effects on depolymerization yield by
changing the reaction temperature and reaction pressure in the
depolymerization step of Step 5 in Example 1. The yield was
demonstrated to be satisfactory at or above the critical
temperature and critical pressure of methanol in the case of using
methanol. The effects of reaction temperature and reaction pressure
were studied under conditions of using 500 ppm of
tetrabutoxytitanium and twice the amount of methanol (weight ratio)
relative to the bottom liquid containing the oligomer supplied for
depolymerization. The results are shown in Table 6 and FIG. 6.
EXAMPLE 10
[0192] A study was made of the effects on yield by changing the
weight ratio of the methanol relative to the bottom liquid
containing the oligomer supplied for depolymerization in the
depolymerization step of Step 5 in Example 1. The study was made
under the conditions of using 1000 ppm of tetrabutoxytitanium, a
temperature of 270.degree. C. and a pressure of 11 MPa. The results
are shown in Table 6.
EXAMPLE 11
[0193] A study was made of the effects on yield by carrying out the
depolymerization step of Step 5 in Example 1 under conditions of
varying residence times and acid values (AV). The results are shown
in Table 6.
TABLE-US-00006 TABLE 6 Depolymerization Reaction Results Residence
AV Temperature Pressure Methanol Catalyst time min. mgKOH/g
.degree. C. MPa weight ratio concentration Ti precipitation Yield %
Effects of 0.5 30 270 11 2 1000 Not observed 48 residence time 1 30
270 11 2 1000 Not observed 66 3 30 270 11 2 1000 Not observed 82 5
30 270 11 2 1000 Not observed 84 10 30 270 11 2 1000 Not observed
85 Effects of AV 5 10 270 11 2 1000 Not observed 85 5 30 270 11 2
1000 Not observed 84 5 60 270 11 2 1000 Observed 80 5 100 270 11 2
1000 Observed 75 5 337 270 11 2 1000 Observed 31 Effects of 5 30
230 11 2 500 Not observed 62 temperature 5 30 250 11 2 500 Not
observed 78 5 30 270 11 2 500 Not observed 83 5 30 290 11 2 500 Not
observed 84 Effects of 5 30 270 6 2 500 Not observed 66 pressure 5
30 270 8 2 500 Not observed 70 5 30 270 11 2 500 Not observed 83 5
30 270 14 2 500 Not observed 84 Effects of 5 30 270 11 1 1000 Not
observed 71 amount of 5 30 270 11 2 1000 Not observed 84 methanol 5
30 270 11 3 1000 Not observed 85 5 30 270 11 6 1000 Not observed 86
Effects of 5 30 270 11 2 0 Not observed 16 catalyst 5 30 270 11 2
100 Not observed 38 concentration 5 30 270 11 2 500 Not observed 78
5 30 270 11 2 1000 Not observed 84 Yield refers to the total yield
of dimethyl adipate and methyl 6-hydroxycaproate.
Tetrabutoxytitanium was used for the catalyst.
INDUSTRIAL APPLICABILITY
[0194] Use of the process of the present invention allows the
obtaining of highly pure 1,6-hexanediol in which the contents of
impurities that lower the polymerization rates during production of
polyurethane and polyester, such as 1,4-cyclohexanediol,
1,5-hexanediol, 1,2-cyclohexanediol, 1,7-pentanediol,
1,5-pentanediol and high boiling point components, are
significantly reduced. In addition, as a result of removing water
and organic acids in the esterification step, Lewis acids and bases
susceptible to water and organic acids can be used in the
depolymerization step without being deactivated, while corrosion of
the reactor can also be inhibited. Moreover, the rate of the
depolymerization reaction can be significantly improved.
* * * * *